The present invention relates to joining and sealing conduits, and, in particular, to joining and sealing conduits of various shapes in areas with a lack of accessibility and visibility.
Conduits, such as ducts, hoses, pipes, tubes and the like are frequently used to transport various fluids, gases or other elements within a structure, such as a vehicle, aircraft or building. Many times the conduits are installed after the structure is partially or totally built, and the conduits must be installed in pieces. The pieces of the conduits then must be joined and sealed after installation.
For example, in the aircraft industry, the environmental control system includes ducts to carry the fluids, gases, air, and the like required to regulate the environment of the aircraft. Typically, the environmental control system ducts are designed and installed after the aircraft is partially or totally built, such that the duct shape must conform to the available space and the ducts must be installed in pieces to avoid structural interferences. As the ducts are installed, nominal one to three inch gaps are generally maintained between the duct segments depending upon the length and material of the duct in order to allow for expansion during operation. Thus, the ducts may be round, elliptical, square, or any other shape that fits in the available space, and the segments of the duct must be joined and sealed in the already congested areas of the aircraft where there is little room to access or view the entire duct joint area.
The conventional manner of joining environmental control system ducts includes bonding elastomeric sheeting, such as flat sheets of silicone impregnated glass, around adjacent portions of the connecting ducts with adhesive, such as Room Temperature Vulcanized (RTV) adhesive. The adhesive must be applied at several locations on the duct system, which is difficult because of the limited space around the duct, the time-sensitive nature of completing the adhesive bond, and the uniqueness of the design of the ducts.
The process of bonding the elastomeric sheeting to join the ducts requires surface preparation, cleaning, multiple supplies, and tools. In addition to the supplies and tools used to apply the sheeting to the ducts, an x-ray machine is also typically used to determine the integrity of the bond between the sheeting and the duct. The x-ray photographs of the joint area reveal where there are voids in the adhesive, uneven application of adhesive, substrate mating pressure, or other issues with the adhesive that may affect the bond between the sheeting and the duct. If the x-rays reveal a problem with the bond, then the installer must remove the sheeting and the adhesive, reapply the adhesive and sheeting, and again x-ray the joint to determine the integrity of the bond. This process must be repeated until the bond between the sheeting and the duct is acceptable.
Once the bond between the sheeting and the duct is acceptable, the elastomeric sheeting is then clamped to the ducts with metal band clamps or tie wraps. The clamps, however, do not provide uniform circumferential pressure to the sheeting covered duct joints, particularly not to the ducts that are square or have some other non-round shape. Thus, when a duct experiences deflection due to internal pressure, the clamp may cause the duct surface to concave, which creates a gap and causes leakage of the elements within the duct. Deflection of the duct also may cause the duct to change shape, which may result in the loosening of the grip of the clamps, a break in the adhesive, and leakage of the elements contained in the ducts. Furthermore, even if the clamps remain tightly in place on the sheeting and ducts, the sharp edges of the clamp may cut into the elastomeric sheeting, particularly as the ducts are subjected to the vibrations, shocks and pressures associated with the operation of an aircraft. Once the clamp cuts into the sheeting, the sheeting will tear and, again, cause leakage of the elements contained in the ducts.
The leaking of the elements contained in the ducts is particularly severe in aircraft that are operated in high humidity or tropical climates because the environmental control system ducts contain high levels of moisture condensation. If the ducts are not completely joined and sealed, the fluid may leak onto electrical systems housed below the ducts and through overhead ceiling panels into the passenger area or body of the aircraft. The moisture release may require a pilot to initiate emergency landing procedures, which includes dumping fuel for a premature landing at the nearest airport.
In order to repair the leaking duct joints, the clamps and sheeting must be removed and the adhesive must be cleaned off of the ducts, which is difficult, time-consuming, and prone to damage the ducts. New adhesive, sheeting and clamps then must be re-applied to the ducts, which is another labor-intensive and time-consuming procedure that is not guaranteed to remedy the problem. In addition, during certain mandatory aircraft maintenance and structural checks, the entire environmental control duct system must be removed and re-installed. After repeated repairs and re-installations, the entire environmental control duct system must be replaced because of the wear and tear on the joint bonding surfaces of the ducts. Therefore, in addition to the time and expense involved in the initial joining and sealing of the ducts, the repairs, re-installation and ultimate replacement is extremely costly because of the human labor and time involved, the loss of flight time for the aircraft, and the cost of replacing the parts of the duct system that cannot be reused after removal.
Thus, there exists a need in the industry for an efficient manner in which to join and seal conduits that have inherent system issues. In particular, there exists a need for an efficient way to join and completely seal conduits of various shapes such that the deflection of the conduit under internal pressure will not cause leakage from the joints, and the joints will not have to be repaired or replaced frequently. Additionally, it would be desirable if the joints may be removed for thorough maintenance checks and reinstalled without an excessive investment of human labor and time, without significant loss of flight time for the aircraft, and without having to replace part or all of the conduit system.